1. Field of the Invention
The present invention relates to apparatus for controlling the alignment and mask to wafer gap distance in an X-ray lithography machine, and more particularly to an alignment and gap control structure employing a cantilevered tip as an integral part of a mask.
2. Description of the Prior Art
U.S. Pat. No. 4,343,993, issued Aug. 10, 1982 to Binnig et al entitled SCANNING TUNNELING MICROSCOPE, disclosed a structure for the investigation of surface structures down to the atomic level. A sharply pointed, electrically conductive tip is placed at a distance on the order of one nanometer from the conductive surface of the sample to be investigated, with an appropriate potential applied across the gap between the tip and surface. As the electron clouds of the atoms at the apex of the tip and at the surface touch, a flow of electrons will result giving rise to a tunneling current which happens to be extremely sensitive to changes in gap width. To render these changes as close as possible to zero, a feedback system controls the distance of the tip from the surface, using the deviations of the tunnelling current from an initial value as a control signal. This control signal is also employed to generate a plot of the topography of the surface being investigated.
U.S. Pat. No. 4,359,892, issued Nov. 23, 1982 to Schnell et al entitled ARRANGEMENT FOR MEASURING SURFACE PROFILES, discloses a surface testing apparatus that includes a bilaminar ceramic flexure element provided with means for generating a voltage which is proportional to the deflection of the flexure element. This amplification is compared with a reference voltage. After amplification, the difference voltage is applied to the flexure element so that the applied force remains constant, independently of the deflection.
U.S. Pat. No. 3,876,879, issued Apr. 8, 1975 to McAdams et al and entitled METHOD AND APPARATUS FOR DETERMINING SURFACE CHARACTERISTICS INCORPORATING A SCANNING ELECTRON MICROSCOPE, discloses a method and apparatus for determining surface characteristics such as elevations of points on a surface wherein; an electron beam scans the surface causing electrons to be emitted from the surface; an electron sensitive detector develops signals in response to the emitted electrons impinging thereupon; a shield is located above the surface for blocking electrons emitted from an area of the surface from reaching the detector, the boundary of the area comprising a line that is a function of the elevation or contour of points on the surface, which line is sensed by the detector as a locus of points on the surface wherein the output of the detector abruptly changes in value.
U.S. Pat. No. 4,516,326, issued May 14, 1985 to Calcagno, Jr. entitled ELECTRONIC DEPTH GAGE, discloses an electromechanical device which uses a digital depth gage micrometer with a probe in combination with a read-out voltmeter to provide automatically recordable profiles of impacted crater sections. The circuit electrically connected to the voltmeter has a Zener circuit which transposes the mechanical movement of the probe to readable and recordable electronic signal information.
U.S. Pat. No. 4,560,880, issued Dec. 24, 1985 to Petric et al entitled APPARATUS FOR POSITIONING A WORKPIECE IN A LOCALIZED VACUUM PROCESSING SYSTEM, discloses apparatus for positioning a semiconductor wafer with respect to a localized vacuum envelope so as to maintain a prescribed gap between the tip of the vacuum envelope and the wafer includes an x-y table, a stage assembly moveable along the z-axis for holding the wafer and a z-axis actuator assembly. The z-axis actuator assembly includes a plurality of fluid-containing bellows coupled between the x-y table and the stage assembly and a hydraulic controller operated by a linear stepper motor for varying the fluid volume in each of the bellows in response to an actuator control signal so as to move the stage assembly along the z-axis. The z-axis actuator assembly can further include a flexible disk positioned in the plane of x-y movement and coupled between the x-y table and the stage assembly for preventing lateral and rotational movement of the stage assembly relative to the x-y table. The positioning apparatus is suitable for use in an electron beam lithography system.
U.S. Pat. No. 4,592,081, issued May 27, 1986 to Eaton et al entitled ADAPTIVE X-RAY LITHOGRAPHY MASK, describes an apparatus for improving alignment accuracy by distorting in a controlled manner an X-ray lithographic mask to compensate for mask distortions induced primarily by thermally induced clamping effects in E-beam and X-ray exposure systems. A system of additional alignment sensors is used to provide localized misalignment information. This information is then used to provide feedback to a servo system which in turn activates electromechanically translatable clamps which distort the X-ray mask so as to minimize misalignment over the exposure field.
U.S. Pat. No. 4,679,326, issued Jul. 14, 1987 to Takizawa et al entitled HEIGHT GAUGE, describes a height gauge that has a touch signal probe provided on a slider vertically movably supported on a support for the purpose of measuring the dimensions or the like of an object by bringing the probe into contact with the object. A rack is formed on the support, and a driving shaft is disposed on the slider, the driving shaft having a pinion engaged with the rack. To the driving shaft are secured a pulley to which the turning force from a motor is transmitted and a control wheel for manually rotating the driving shaft. A clutch member is interposed between the pulley and the control wheel. When the clutch member is engaged with the pulley, the slider is automatically moved up and down, while when the clutch member is engaged with the control wheel, the slider can be manually moved up and down. The height gauge further includes a control circuit which stops the drive of the motor when the touch signal probe generates a touch signal and which holds the indication of a measured value being displayed at that time.
U.S. Pat. Re. 33,387, issued Feb. 9, 1988 to Binnig entitled ATOMIC FORCE MICROSCOPE AND METHOD FOR IMAGING SURFACES WITH ATOMIC RESOLUTION, describes a system wherein a sharp point is brought close to the surface of a sample to be investigated so that the forces occurring between the atoms at the apex of the point and those at the surface cause a spring-like cantilever to deflect. The cantilever forms one electrode of a tunnelling microscope, the other electrode being a sharp tip. The deflection of the cantilever provokes a variation of the tunnel current, and that variation is used to generate a correction signal which can be employed to control the distance between said point and the sample, in order, for example, to maintain the force between them constant as the point is scanned across the surface of the sample by means of an xyz-drive.
U.S. Pat. No. 4,785,189, issued Nov. 15, 1988 to Wells entitled METHOD AND APPARATUS FOR LOW-ENERGY SCANNING ELECTRON BEAM LITHOGRAPHY, describes a system wherein an electron sensitive surface is patternized treated to a high resolution pattern of low-energy electrons without any need to do focussing by emitting the low-energy electrons from a pointed electrode and positioning the apex of the pointed electron emitting source suitably close to the surface being treated.
U.S. Pat. No. 4,806,755, issued Feb. 21, 1989 to Dverig et al and entitled MICROMECHANICAL ATOMIC FORCE SENSOR HEAD, describes a micromechanical sensor head designed to measure forces down to 10.sup.-13 N. It comprises a common base from which a cantilever beam and a beam member extend in parallel. The cantilever beam carries a sharply pointed tip of a hard material, dielectric or not, for interaction with the surface of a sample to be investigated. Bulges forming a tunnelling junction protrude from facing surfaces of said beams, the gap between said bulges being adjustable by means of electrostatic forces generated by a potential (V.sub.d) applied to a pair of electrodes respectively coated onto parallel surface of said beams. The sensor head consists of one single piece of semiconductor material, such as silicon or gallium arsenide (or any other compounds thereof) which is fabricated to the dimensions required for the application by means of conventional semiconductor chip manufacturing techniques.
U.S. Pat. No. 4,870,668, issued Sep. 26, 1989 to Frankel et al and entitled GAP SENSING/ADJUSTMENT APPARATUS AND METHOD FOR A LITHOGRAPHY MACHINE, discloses a step and repeat mechanism used with an X-ray lithography system for moving a wafer to be exposed from position to position beneath the source of X-rays. The step and repeat mechanism includes means for moving the wafer to be exposed with six degrees of freedom. Conventional drive motor means move the step and repeat mechanism, and wafer held thereby, in the X, Y and Z linear directions, as well as rotates, tip and tilt the wafer in the planar direction. In addition, the system includes three fine Z motor assemblies for moving the wafer in fine increments in the Z direction, which motor assemblies are used to tip and tilt the plane of the wafer. Sensors are included for determining the plane of the mask and the plane of each of the various sections of wafer to be exposed, so that appropriate tip and tilt adjustments by the three fine Z motor assemblies can be made to cause the average plane of each section of the wafer to be exposed to be parallel to the plane of the mask. All of the moving mechansism, with the exception of the Y direction moving mechanism, are affixed the same level of the step and repeat mechanism. Included in the mechanism is a substage plate which is adjusted by the three triangularly positioned fine Z motor assemblies.
U.S. Pat. No. 4,874,945, issued Oct. 17, 1989 to Ohi and entitled ELECTRON MICROSCOPE EQUIPPED WITH SCANNING TUNNELING MICROSCOPE, discloses an electron microscope equipped with a scanning tunneling microscope. The electron microscope comprises a holder, a scanning tunneling microscope scanner having a tip, and a shift mechanism. A sample is fixed inside the holder that is mounted between the upper pole piece and the lower pole piece of an objective lens. The shift mechanism moves the scanner in two directions parallel to the surface of the sample and in a direction vertical to the sample surface. The tip is poised above a desired portion of the sample by driving the shift mechanism while observing the tip and either a reflection electron microscope image or a transmission electron microscope image of the sample. Then, the scanner uses the tip to scan the sample surface to obtain a scanning tunneling microscope image.
U.S. Pat. No. 4,943,719, issued Jul. 24, 1990 to Akamine et al entitled MICROMINATURE CANTILEVER STYLES, discloses a technique wherein integral sharp tips on thin film cantilevers are produced by forming a rectangular silicon post on a silicon wafer. Etching the top of the post leaves sharp silicon tips at the corners of what remains of the silicon post. A silicon dioxide contilever with an integral tip is thermally grown over the silicon wafer and the sharp silicon tips.